1. Field of the Invention
The present invention relates to a method of and a member for adding a treating agent in a molten-metal treating process, for example, desulfurization or deoxidation, or in a component adjusting process.
2. Description of the Prior Art
In the case of desulfurization, for example, recently the requirements for limitation on sulfur content (hereinafter referred to as S content) have become very severe, and depending on applications, a so-called low-sulfur steel with an S content of less than 50 ppm is demanded. Therefore, with the present-day steel making method using a blast furnace-converter system, and theoretically, it is necessary to carry out sufficient desulfurization in the converter, that is, on the stage prior to steel making, so as to prepare a molten metal with an S content below the limit which allows refining in the steel making process. On the other hand, the circumstances of materials in the blast furnace are assuming an aspect which does not warrant optimism, making it difficult to obtain a molten metal with an S content below the refinable limit as described above.
It is the outside-furnace desulfurization of molten iron that has made its advent as the most effective method of pre-treatment of or low-sulfur steel making from a molten metal which has a high S content due to such circumstances of the blast furnace. At present, various outside-the-furnace desulfurization systems have been invented and put to use. For example, the addition and agitation method, blowing-in method, etc. are usually employed.
The addition and agitation method uses a plunging member to plunge a desulfurizing agent and auxiliary agent packed in a drum can or the like into molten steel taken out into a ladle and agitate the same. With this, however, the initial cost is high owing to the installation of the drive unit, etc., and on top of this, the plunging member has to be frequently replaced since it can be easily melt-wise damaged, thus involving high running cost. Further, the sulfur which has once floated up to the surface of the melt as a slag tends to return to the molten steel or some of the desulfurizing agent and auxiliary agent burn out before they reach suitable positions in the molten steel, so that more amounts of desulfurizing agent and auxiliary agent than is necessary are consumed.
According to the blowing-in method, after a desulfurizing agent and auxiliary agent are charged into molten steel by a plunging member or the like, desulfurization is carried out by blowing N.sub.2 gas into the molten steel with the ladle sealed. In this case also, drawbacks similar to those described above in connection with the addition and agitation method remain unsolved.
In brief, in the conventional methods, the yield of a desulfurizing agent and its auxiliary agent (hereinafter referred to as treating agent) is generally low and the treating operation requires a long residence time (20-25 minutes), involving a loss of the thermal energy of the molten steel. Further, what should be particularly noted is that while recent researches have developed various types of desulfurizing agents, no decisive method of use, or addition, of such agents has been established. As a result, the costs of expensive installation and replaceable members such as plunging members and the useless consumption of more than necessary amount of treating agent have extremely raised the initial cost and the running cost.
Further, since a large amount of treating agent is charged into molten steel at a single place therein, the resulting chemical reaction is violent, involving danger and producing smoke and dust in large amounts, incurring the possibility of causing environmental pollution, such as air pollution. On top of this, the treating effect is good only at the charged place and agitation for a prolonged period of time is required in order to uniformly distribute the treating effect throughout the molten metal in the ladle.
Further, referring to the outside-the-furnace deoxidizing of molten steel, among the most general methods of adding a deoxidizing agent is one in which it is formed into a lump which is then charged into molten steel and another in which it is formed into a shell which is then shot into molten steel. With these methods, however, the deoxidizing agent tends to burn or float up (depending upon specific gravity) before it produces chemical reactions in the molten steel for deoxidation and hence it has been usual practice to charge more than the necessary amount of treating agent but the scattering of deoxidation yield cannot be avoided. Thus, in the conventional methods, stabilized deoxidation yield cannot be obtained despite the use of a large amount of treating agent.